Fix build failure in ioserver

Change-Id: I2b8bf356ea8e9c62a0e23ff2ce333e963fd320c1
Reviewed-on: http://review.couchbase.org/44437
Reviewed-by: Subhashni Balakrishnan <b.subhashni@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>